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Leaded Racing Fuels | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Paul Barrows
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What's the Difference in Leaded Race Fuels? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Definitions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
MOTOR OCTANE: (a) CFR Tested @ 900 rpms, timing is varied with compression ratio, fuel is preheated to 300deg, intake air is preheated to 100deg. (b) Motor Octane, measured under varying load is definitely the most representative octane measurement for REAL WORLD HI-PERFORMANCE ENGINE APPLICATIONS.
R+M OCTANE (R+M): (a) this method of measurement consists of adding together both Motor and Research Octaneâs then dividing them by two. (b) This is the number in the yellow box, which you see at the gas pump. (c) This number should only be used in determining which octane to use in your stock street car or tow vehicle. RESEARCH OCTANE (RON): (a) CRF tested @ 600rpms, fixed timing at 13deg BTDC, fuel pump is not controlled and Intake air is varied with the barometric pressure. (b) This is basically a no-load test and this number should not be used in determing which fuel to use in your race engine. SPECIFIC GRAVITY (SG): (a) This is the weight of fuel compared to water, water being 1.00. If race fuel were .750 (SG) it would weigh and the weight of water. (b) The less dense the fuel (lower specific gravity) the higher the BTU content, and the better the stability of the fuel at higher RPMâs. (c) The lower the specific gravity of the fuel, the more crucial the jetting becomes, and the easier it becomes to run lean. (d) The combustion speed is determined primarily by the (density) of the fuel mixture. (e) The higher the specific gravity, the cooler the fuel charges. OCTANE DIFFERENTIAL (OD): (a) Octane Differential (OD) is the number of the octane points between motor and research Octane. The trend has shown that the lower the (OD) the more consistent the fuel, and that more power will be produced. (b) As a rule of thumb, fuels with the (OD) number below 7.0 are better suited for serious racing applications, where as 7.0 and higher (OD) numbers are generally used for Low to Mid Performance racing engines. CONSISTENCY (a) it is very important that the fuel you use maintains its purity and consistency regardless of which brand you use. Try not to buy fuel that has been stored in a bulk storage tank, or transferred from one bulk location to another. Bulk fuel storage tanks have a tendency to sweat or secrete moisture, Therefore changing the consistency or purity of the fuel. If at all possible buy your fuel in a factory sealed drum (The cost is usually higher) but itâs well worth it in the long run. |
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